1. Field of the Invention
The present invention relates to an optical system shifting device for a camera in which an optical system, such as a photo-taking lens, etc., is shifted in the direction of the optical axis for varying the focal distance, etc.
2. Description of the Prior Art
Various types of optical system shifting devices for a camera have been proposed heretofore. These include a photo-taking lens which can be housed within the camera body for assuring compactness in size of the camera so as to facilitate its handling, or an optical system, such as a photo-taking lens, etc., which is made to be freely movable in the direction of the optical axis for varying the focal distance. The movement of the optical system is capable of being effected automatically by the driving force of a motor.
FIG. 1 shows an example of this kind of optical system shifting device, wherein, when a changeover lever 1 is rotated manually in the clockwise direction, a gear 4 and a tele-wide gear 5 engage with each other, and, at the same time, a switch 7, which is to rotate a motor 6 in the reverse direction, is placed in the ON state. As a result of this, the driving force of the motor 6 is transmitted through a gear train shown in the drawing and a gear 3 and a gear 4 of the changeover lever 1 to the tele-wide gear 5. Then, a rotating pin 9, within an elongated hole 8a of an arm 8, which rotates in the direction of an arrow shown in the drawing along with a rotation of the tele-wide gear 5, shifts and retreats the arm 8 together with a lens barrel 10 in the direction of the optical axis as shown by an arrow in the drawing. Meanwhile, a roller 1 comes out of a tele-cam 8b of the arm 8 and rides over a cam part 8c. The state will be maintained. After that, when the rotating pin 9 reaches the rearmost position, the roller 11 drops into a wide-cam 8d, thereby rotating the changeover lever 1 in the counterclockwise direction by the action of a spring 2. The engagement between the gear 4 and the tele-wide gear 5 is discontinued while, at the same time, the switch 7 is placed in an OFF state and rotation of the motor 6 stops so that positioning of the lens barrel 10 which holds a lens 10a may be carried out.
Also, while an explanation is provided on the pulling-in of the lens barrel 10 in the above description, at the time of pulling-out, as the rotating pin 9 rotates from the rearmost position to the foremost position, the pulling-out and positioning of the lens barrel 10 will be made in a manner similar to that which is mentioned above.
However, in this kind of optical system shifting device, the positioning of the lens barrel 10 to a prescribed position depends, as shown in FIG. 1, on the changeover timing of a clutch consisting of the changeover lever 1, etc., and on the timing of the ON-OFF positioning of the switch 7 for driving the motor 6. Therefore, precision in the setup of such components has to be maintained at a high level, thus increasing difficulty in manufacture. Also, as the rotating pin 9 and a sliding part of the elongated hole 8a serve concurrently for driving and positioning of the lens barrel 10, problems with regard to the components being placed in an engaged state when shifting of the lens barrel 10 stops, thus impairs the smooth movement thereof at the time when the lens barrel 10 starts shifting again.
Further, when the lens barrel 10 is pulled forward by an external force, as shown in FIG. 1, such a force, preventing counterclockwise rotation in the direction shown by the arrow in the drawing, will be imparted to the tele-wide gear 5 through the elongated hole 8a and the rotating pin 9, and, as a result of this, the gear 4, which tends to rotate the gear 5 in the counterclockwise direction, rotates the changeover lever 1 by an increase in the reaction force thereof in the counterclockwise direction which is the direction shown by the arrow in the drawing. Therefore, the roller 11 provided at the changeover lever 1 will push strongly on a side of the arm 8.
Therefore, when an external force, such as may be applied by the hand of an operator, acts inadvertently on the lens barrel at the time when the lens barrel is pulled in, a strong force will act in a direction other than the direction of the optical axis of the lens, thus creating the problem of eccentricity and imparting an inclination to the lens.
Also, even if the gear 4 rotates in the counterclockwise direction, contrary to the above-mentioned case, when the lens barrel 10 is pushed in by an external force at the time of pulling-in of the lens barrel, the tele-wide gear 5 tends to rotate further in the clockwise direction, thus increasing the counterclockwise rotation of the gear 4. Therefore, the rotating force of the changeover lever 1 in the direction of the arrow shown in the drawing increases, and, in this case, the roller 11 also strongly pushes on a side of the arm 8.
Also, as in the case of pulling-out the lens barrel 10 which is considered to be on the same level, the side of the arm 8 will be pushed strongly by the roller 11 depending on the direction of the external force that is working on the lens barrel 10.
Also, the kinds of optical system shifting devices mentioned above have problems such that an operator has to operate an actuating switch, thus taking his or her eyes off the viewfinder depending upon the position of the actuating switch. This constitutes troublesome handling of the camera, and, at the same time, when a shock through an external force works on the lens barrel as the shifting stops, the shock also affects the driving system thereof, which could cause damage to the optical system of the lens barrel, and, therefore, to the driving system.
Therefore, the lens barrel or a driving mechanism could be reinforced so as to withstand such shocks, but it would involve having a more complicated mechanism as well as increasing the weight and/or size.